html,
body {
    margin: 0;
}

* {
    box-sizing: border-box;
}

ul,
li {
    margin: 0;
    padding: 0;
}

li {
    list-style: none;
}

a {
    text-decoration: none;
}

main {
    display: flex;
    flex-direction: row;
    align-items: center;
    justify-content: center;
    width: 100vw;
    height: 100vh;
    position: relative;
    background: #2c3a47;
    z-index: 25;
}

ul {
    display: flex;
}

ul li {
    margin: 0 18px;
}

li a {
    /* 定位格式   */
    position: relative;
    display: block;
    /*    颜色*/
    color: white;
    /* 宽高字体大小   */
    width: 64px;
    height: 64px;
    font-size: 36px;
    text-align: center;
    line-height: 66px;
    border-radius: 50%;
    /*   background:#2c3a; */
    background: #2c3a47;
    transition: 0.6s;
    /*过渡时间*/
}

li a:hover {
    text-shadow: 0px 0px 4px #25ccf7;
    /*  水平偏移 垂直偏移 模糊程度 颜色  */
}

li a::before {
    content: '';
    position: absolute;
    width: 100%;
    height: 100%;
    top: 0;
    left: 0;
    border-radius: 50%;
    background: #25ccf7;
    /*     background:red; */
    z-index: -1;
    transition: 0.6s;
    transform: scale(0.8);
}

li a:hover::before {
    box-shadow: 0 0 14px 2px #25ccf7;
    transform: scale(1.05);
}


/* bilibili */

.svg-icon {
    transition: 0.6s;
    /*   filter:invert(1);//滤镜效果：使用背景色的反色 */
    /*   filter:brightness(100);//将图片转化为白色 */
    /*   filter: brightness(0);//图片转化为黑色 */
    filter: brightness(0) invert(1);
    /*图片转化为黑色,再反转为白色*/
}

li a:hover .svg-icon {
    filter: brightness(100) drop-shadow(0px 0px 4px #25ccf7);
    /*drop-shadow对图片的投影*/
}


/*  */

li a .iconfont {
    position: relative;
    display: block;
    width: 64px;
    height: 64px;
    font-size: 36px;
}